The present invention concerns a brake assembly for a cyclists"" training device, which has an application in the sports equipment and leisure sector.
More particularly, the brake assembly in question is intended to be advantageously mounted on training devices, for example of the type used by cyclists, which can be used both in the open, for example in order to warm up muscles before a cycling race, and in homes or gyms for example when the atmospheric conditions are such that normal cycling activity is impossible.
At present, various training devices for cyclists provided with a brake assembly of the type in question are available on the market, all of said devices essentially comprising a support frame provided with a clamp for fixing the hub of the rear wheel of a bicycle so that the wheel rotates in contact with a horizontal roller of the brake assembly.
Generally, the brake assembly also has suitable resistance means acting on the roller in order to simulate a resistance to forward movement and adjusting means associated with the resistance means, for varying the intensity of the abovementioned resistance.
As is known, the resistance means may be of the mechanical, electrical, hydraulic or magnetic type depending on the physical principle which is adopted in order to oppose rotation of the roller by means of a resistive torque acting against rotation thereof.
Mechanical resistance means are generally excessively noisy and do not operate in an entirely satisfactory manner since they do not allow application of a resistive torque proportional to the speed of rotation, as instead would be desirable.
Resistance means of the hydraulic type are able to simulate more effectively the resistive torque applied to the roller upon variation in the pedaling speed and, in accordance with the embodiment illustrated in international patent application No. PCT/EP96/04861 in the name of the same applicant, are generally provided with a chamber containing a viscous fluid in which a rotor mechanically connected to the roller is immersed.
This constructional solution has proved in practice to be excessively complex, costly to produce and difficult to assemble.
As is known, with resistance means of the electrical type it is possible to vary in a more suitable manner the resistive torque applied. Said means generally envisage the use of an excitation coil which is mounted fixed on the training device and supplied with direct current in a controlled manner so as to generate a magnetic field, the flux lines of which extend radially outwards preferably conveyed by electromagnetic disks with radial teeth.
A disk mechanically connected to the transmission of the device, so as to be made to rotate by the action of the cyclist on the pedals, is rotatably mounted on the outside of the coil. The disk, when rotating about its axis, passes through the magnetic field lines produced by the coil and consequently causes the generation of parasitic currents able to oppose rotation of the disk, exerting a braking torque having an intensity dependent upon the current applied to the coil.
These known braking devices of the electromagnetic type are described and claimed for example in the U.S. Pat. No. 5,042,794 and U.S. Pat. No. 5,072,930 and have the drawback that they require a power supply drawn from a power socket with mains voltage and therefore are not very suitable for use in external environments.
Such type of use is, however, desirable and useful for athletes who need to perform a warm-up in the open, for example before a race, or for ordinary users who wish to train in a garden, at a campsite or at the seaside, where power sockets are not available.
Moreover, from a constructional point of view they are excessively complex and disadvantageous from a cost point of view.
In accordance with the embodiment described in the patent EP-A-603,454, the magnetic resistance means envisage the generation of a resistive torque by causing the rotation of a disk of paramagnetic material which is rigidly connected to the roller rotation shaft inside a magnetic field produced by two opposite series of permanent magnets mounted on two support disks facing each other and fixed with respect to the rotating disk.
Adjustment of the intensity of the field between the disks and therefore of the resistive torque produced by the field as a result of the parasitic currents induced in the rotating disk is performed by varying the relative position of the two series of magnets, achieved by varying the relative angular position of the two disks supporting the said permanent magnets.
In practice, this embodiment has been unable to ensure an adequate resistive torque. Moreover, it necessarily envisages the use of a second rotating disk of heavy material having the function of a flywheel in order to increase the moment of inertia of the device. In addition to this, this known solution is excessively complex from a constructional point of view and difficult to assemble.
In the U.S. Pat. No. 5,051,638 the magnetic field is created between two cylindrical plates of ferromagnetic material, one of which is fixed and has mounted thereon a plurality of permanent magnets and the other of which is rotating and has fixed thereon a disk of conductive paramagnetic material, such as, for example, aluminum or copper.
In this case also, it is necessary to envisage the use of a second rotating disk as a flywheel in order to increase the moment of inertia of the brake assembly.
Entirely similar embodiments are also contained in the patents NL 1008474 and U.S. Pat. No. 5,586,624. In particular, this latter patent describes and illustrates a solution in which advantageously the same rotating plate of ferromagnetic material, which in this case supports aluminum sheets, also acts as a flywheel for the assembly and for this purpose has a suitable weight and dimensions.
In both the embodiments contained in the two patents NL 1008474 and U.S. Pat. No. 5,586,624, adjustment of the magnetic field and therefore the resistive torque is obtained by varying the distance of the disks between which the magnetic field is produced.
In this situation, the main object of the present invention is therefore that of providing a brake assembly for a cyclists"" training device, which is constructionally simple, low-cost and easy to assemble and is able to achieve an effective resistive torque with an optimum action upon variation in the force exerted by the user.
Another object of the present invention is that of providing a brake assembly for a cyclists"" training device which is completely silent.
A further object of the present invention is that of providing a brake assembly for a cyclists"" training device which allows easy and selective adjustment of the force required of the user.
These objects, together with others which will be clarified more fully below, are achieved by a brake assembly, in particular for a cyclists"" training device, comprising: a support structure, a shaft rotatably mounted on the support structure and provided with a first portion capable of being rotationally driven by the action of a user and a second portion provided with magnetic means able to exert a resistive torque on the shaft.
According to the invention the assembly is characterized in that the magnetic means comprise in turn: at least one rotor keyed onto the shaft and having, fixed thereon, one or more permanent magnets; and at least one stator mounted on the support structure in the vicinity of the rotor and comprising a disk of ferromagnetic material and a shaped plate of substantially conductive and non-magnetic material which is fixed to the ferromagnetic disk and physically located between the rotor and the ferromagnetic disk; the rotation of the shaft and consequently the rotor being able to produce, as a result of the action of parasitic currents generated on the stator, a resistive torque able to oppose rotation of the shaft itself.
Owing to this invention, the brake assembly may be produced at very low costs and may be easily mounted on training devices, in particular for cyclists, intended to be used both in closed environments and in open environments.